This invention generally relates to phased array antennas and, in particular, to a method and apparatus for a digital phased array radar antenna.
Phased array antenna systems generally employ fixed, planar arrays of individual, or subarrays of, transmit and receive elements. Phased array antennas receive signals at the individual elements and coherently reassemble the signals over the entire array by compensating for the relative phases and time delays between the elements. For transmission, the relative phase compensation is applied to the signals at each of the individual elements to electronically steer the beam.
In conventional phased array antennas, the phase shifts and time delays are applied in the analog domain. Typically, the received signals are combined across an array using analog microwave combining circuits and down-converted to an intermediate frequency using analog microwave mixer components. The intermediate frequency is further processed in the analog domain prior to digitization at a low baseband frequency. This analog processing approach is generally not applicable to large arrays, since wide-bandwidth signals do not retain phase coherency over large arrays. Wideband signal processing in large phased arrays requires programmable true-time-delay components to combine the wideband signals over the array. Programmable, analog, true time delays are generally large, complex and costly components.
To help solve this problem for wideband signals, digital processing of the antenna signals has been attempted. This process typically involves digitally processing the received signals at an intermediate frequency. This digital solution requires high precision, high speed, analog-to-digital converters with large power demands to digitize the intermediate frequency.
In accordance with the present invention, the disadvantages and problems associated with previous phased array antennas have been substantially reduced.
In particular, the present invention provides a method and apparatus for a digital phased array antenna. The digital phase array antenna comprises a plurality of antenna elements, each element receiving an incoming signal, and an analog-to-digital converter coupled through RF amplification and matching circuitry to at least one of the antenna elements to convert the incoming signal to a multi-bit digital signal. Also included is a demodulator or de-ramp circuit coupled to the analog-to-digital converter for reducing the bandwidth of the multi-bit signal.
Also in accordance with the present invention, a method for processing a received incoming signal at a digital phase array antenna is provided. This method comprises receiving an incoming signal at an antenna element. The signal is converted to a multi-bit digital signal and the bandwidth of the multi-bit signal is reduced in the digital domain.
Further in accordance with the present invention, there is provided an RF module comprising radio frequency circuitry receiving a signal from at least one antenna element and amplify the signal. The RF module also includes digital transmit and receive circuitry coupled to the radio frequency circuitry. The digital transmit and receive circuitry includes an analog-to-digital converter for converting the signal to a multi-bit digital signal.